The role of the subtropical North Atlantic water cycle in recent US extreme precipitation events
The role of the subtropical North Atlantic water cycle in recent US extreme precipitation events
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DOI：
10.1007/s00382-017-3685-y
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发表时间：
2018-02
期刊：
影响因子：
4.6
通讯作者：
Laifang Li;R. Schmitt;C. Ummenhofer
中科院分区：
文献类型：
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作者：
Laifang Li;R. Schmitt;C. Ummenhofer
分析了海洋水循环在2015年美国创纪录的暖季降水中所起的作用。极端降水从春季开始于美国南部，并于2015年夏天向北传播到中西部和五大湖地区。这种降水异常的季节演变代表了美国暖季降水的典型变率模式。对大气水汽通量的分析表明，这种降水模式与副热带北大西洋的水汽输出有关。春季，美国南部降水过多是由于副热带北大西洋西北部的水汽通量增加所致。北大西洋水汽通量与当地土壤水分相互作用，使得美国中西部在夏季从墨西哥湾吸收了更多的水分。进一步的分析表明，近几十年来，降雨模式与北大西洋水循环之间的关系变得更加重要，这表明出现像2015年那样的极端情况的可能性增加。事实上，1993年和2008年这两次创纪录的暖季降水事件都发生在66年分析期的最近几十年。从北大西洋输出的水留下了明显的表面盐度特征。盐度特征出现在本研究分析的所有三个极端降水事件之前的春季，即春季北大西洋副热带地区盐度高于正常水平，然后是夏季中西部极端降水。与1993、2008和2015年不同的海温异常模式相比，盐度异常在这些极端洪涝年的空间分布更加一致。因此，我们的研究表明，季前盐度模式可以用于改进对中西部极端降水的季节性预测。
The role of the oceanic water cycle in the record-breaking 2015 warm-season precipitation in the US is analyzed. The extreme precipitation started in the Southern US in the spring and propagated northward to the Midwest and the Great Lakes in the summer of 2015. This seasonal evolution of precipitation anomalies represents a typical mode of variability of US warm-season precipitation. Analysis of the atmospheric moisture flux suggests that such a rainfall mode is associated with moisture export from the subtropical North Atlantic. In the spring, excessive precipitation in the Southern US is attributable to increased moisture flux from the northwestern portion of the subtropical North Atlantic. The North Atlantic moisture flux interacts with local soil moisture which enables the US Midwest to draw more moisture from the Gulf of Mexico in the summer. Further analysis shows that the relationship between the rainfall mode and the North Atlantic water cycle has become more significant in recent decades, indicating an increased likelihood of extremes like the 2015 case. Indeed, two record-high warm-season precipitation events, the 1993 and 2008 cases, both occurred in the more recent decades of the 66 year analysis period. The export of water from the North Atlantic leaves a marked surface salinity signature. The salinity signature appeared in the spring preceding all three extreme precipitation events analyzed in this study, i.e. a saltier-than-normal subtropical North Atlantic in spring followed by extreme Midwest precipitation in summer. Compared to the various sea surface temperature anomaly patterns among the 1993, 2008, and 2015 cases, the spatial distribution of salinity anomalies was much more consistent during these extreme flood years. Thus, our study suggests that preseason salinity patterns can be used for improved seasonal prediction of extreme precipitation in the Midwest.